Power electronics refers to the application of solid-state electronics related to the control and conversion of electrical power. This conversion is typically performed by Silicon, Silicon Carbide, and Gallium Nitride devices that are packaged into power modules. One of the factors associated with the power modules is that they tend to generate heat. While the heat generated by the device is due to many factors, it generally relates to the fact that the device efficiency is always less than 100%, and the efficiency loss typically becomes heat. Unfortunately, device performance tends to erode with increased temperatures and at certain temperature thresholds the device is destroyed.
An additional factor for thermal management relates to the packaging of a number of devices in small footprints. The power density at which the devices, and thus the module can operate, therefore depends on the ability to remove this generated heat. For many applications, including military and commercial aviation power electronics, the highest possible power density is needed.
The most common form of the thermal management of power electronics is by heat sinks. Heat sinks operate by transferring the heat away from the heat source thereby maintaining a lower temperature of the source. There are various types of heat sinks known in the thermal management field including air cooled and liquid cooled devices.
One example of the thermal management of a power module includes the attachment of a heat sink with embedded tubes to provide liquid cooling of the power module. The heat sink is typically a metallic structure, such as aluminum or copper. The tubes are generally metallic as well, with copper being the most common material. Some substance in liquid form, such as water, is passed through the tubes, and subsequently passes through the tubes in the structure. Typical tube outside diameters (ODs) are ½″, ⅜″, and occasionally as small as ¼″. Due to turn radius and pressure limitations, there are usually no more than 4 to 6 tube passages per six-inch width.
The heat sink is typically coupled to the power module base with a thermal interface material (TIM) dispersed there-between. The thermal interface material may comprise thermal greases, compliant thermal pads, or the like. Although a relatively good thermal contact is accomplished, the thermal interface material has certain thermal resistance, which is disadvantageous to heat exchange between the heat sink and the heated surface. The thermal interface material is a better thermal conductor than air, but still tends to be the largest single component of thermal resistance between the heat source and the liquid cooling.